The invention relates to thrust reversers for aircraft turbojet engines. In particular, the invention relates to an aircraft thrust-reverser turbojet-engine having an external pod which combines with an internal stationary structure to define an annular duct through which circulates a bypass flow. The thrust reverser includes vane cascades in the pod and at least one displaceable fairing mounted on the pod in a manner to be displaceable along a plurality of guides. The fairing is movable between a stowed position wherein it blocks access to the vanes and a deployed position wherein the vanes are exposed. Drive devices are provided to drive the displaceable fairing relative to the pod and flaps are arranged to seal the annular duct when the displaceable fairing is in the deployed position in order to deflect the bypass flow towards the vane cascades.
When the turbojet engine operates in a forward thrust mode, the displaceable fairing constitutes all or part of the pod""s downstream end, the flaps in this case being housed within the displaceable fairing which seals off the bypass flow from the vane cascades. The displaceable fairing is arranged to be axially moved rearward by a control system illustratively comprising linear actuators affixed upstream of the vane cascades. Rearward motion of the displaceable fairing urges the plurality of flaps to pivot and thereby seal the duct to deviate the bypass flow through the duct towards the vane cascades configured along outer periphery of the duct. The vane cascades are therefore only accessible when the displaceable fairing is in the deployed position.
In known embodiments of such turbojet-engine thrust reversers, each comprising a semi-cylindrical segments of the displaceable fairing is connected to a displacement drive means illustratively comprising two linear actuators. The flaps are pivoted, for example, by linkrods connected to a fixed linkrod pivot positioned along the inside wall of the bypass duct.
European patent document 9 109 219 A discloses illustrative embodiments of such thrust reversers. FIGS. 1 and 2 schematically show the configurations of the thrust-reverser components as described in European patent document 9 109 219 A.
The pod 1 enclosing the bypass flow from the fan and the inner engine stationary structure 2 combine to subtend an annular duct 3 through which passes the bypass flow F2. The pod 1 and the stationary inner structure 2 are supported by a pylon 4 underneath the aircraft""s wing. The pod 1 comprises an upstream portion terminating downstream into a rigid framework 5, and further comprises along a downstream side thereof a displaceable fairing 6 consisting of two semi-cylinders 6a, 6b, each bounded by an inner wall 7 bounding in turn the cold flow F2, and an external wall 8 implementing the displaceable streamlined contour of the pod 1. The two walls 7, 8 diverge in the upstream direction to define therebetween an annular duct 9 fitted with a set of cascaded vanes firmly affixed to the framework 2. Linear actuators 10a, 10b are provided to implement the axial displacements of the semi-cylinders 6a and 6b. Flaps 11 hinge upstream on the inner wall 7 and downstream on linkrods 12, the linkrods in turn hinging on the inner structure 2. The flaps 11 are housed within the semi-cylinders 6a, 6b when positioned close to the framework 5. When the displaceable fairing 6 assumes this upstream position in the stowed position, the vane cascades are enclosed within the space 9.
When the linear actuators 10a, 10b extend axially, the fairing 6 translates downstream and the vane cascades are exposed to the bypass flow. The linkrods 12 pivot on their pivots 13 and the flaps 11 move to block the annular duct 3 downstream from the vane cascades. The bypass flow F2 is deflected toward the van cascades which in turn deflect the flow F2 to the front of, and outside of the pod.
The semi-cylinders 6a, 6b are mounted in a sliding manner in guides 14a, 14b, 14c, 14d positioned near the pylon 4 and near a spacer 15 which is diametrically opposite the pylon 4. The pylon 4, the spacer 15 and the framework 5 are firmly affixed to the stationary inner structure 2.
In the described thrust reverser, the guides 14a, 14b, 14c, 14d operate in at least three basic modes. The first mode allows engaging the structures of the displaceable fairing 6. The second mode is to guide the displaceable fairing 6 in a direction parallel to the engine axis when the displaceable fairing is moved. The third mode is to resist the aerodynamic stresses applied to the structure of the displaceable fairing 6 that tend to separate the structure from the inner structure 2 enclosing the engine. Two stresses are applied to the displaceable fairing 6, namely one longitudinal and the other radial. These stresses are absorbed in guide elements 14a, 14b, 14c, 14d configured at each radially upper and lower end of the stationary structure 2.
Illustratively, there are two linear actuators 10a, 10b for each half of the displaceable fairing 6a, 6b. It should be noted that there may be additional actuators used in the thrust reverser system. The linear actuators serve at least three basic functions in this type of thrust reverser. The first function is to drive the displaceable fairing 6. The second function is to transmit, at least partly, the stresses applied to the displaceably fairing 6 by means of the framework 5 to the upstream stationary structure of the pod 1. The third function is to provide a safer locking system for the structure.
Each linear actuator 10a, 10b is configured a distance L away from the nearest guide element 14a, 14b, 14c, 14d. This distance L entails torque generating stray forces in the stationary structure 2 and in the displaceable fairing 6a, 6b. To remedy this problem, the guide elements 14a, 14b, 14c, 14d may be extended. This design would generally require structural elements that protrude outside the streamlines of the pod 1. One might also structurally reinforce the guide elements by increasing their cross-sections. Such a solution however would entail an increase in weight. Highly accurate synchronization between the linear actuators 10a, 10b might partly compensate the problem, but such remedies entail two substantial drawbacks; the first one being a drop in thrust-reverser reliability and the second one being an increase in weight.
Additional drawbacks are incurred on account of configuring the linear actuators 10a, 10b in the zones of the annular space 9 which are between the pylon 4 and the spacer 15, the zones being covered by those vane cascades deflecting the flow F2 that are near the front of the pod 1. The bypass flow F2 through the pod 1 therefore is partly blocked by the linear actuators 10a, 10b. This loss of cross-section therefore must be compensated by a greater axial length of the set of vane cascades, whereby retraction of the displaceable fairing 6 is affected. The cases of the linear actuators 10a, 10b are subjected to buckling stresses from the reverse flow F2. As a result, the cross-section of the structure of the linear actuators 10a, 10b must be increased, with an attending increase in weight. During thrust reversal of the turbojet-engine, the drive rod of the linear actuators is positioned within the flow F2 and therefore subjected to pollution which must be counteracted using a sophisticated sealing system. The exposure of the drive rod to the bypass flow affects linear-actuator weight and reliability. Moreover, in configuring the size of the vane cascades, the obstruction represented by the linear actuators in order to compensate the lost radial reversal cross-section must be taken into account. As a result, it is difficult to use identical vane cascades and their manufacture is more costly. Lastly, the increase in friction between the guide elements caused by the torque requires a structurally reinforced framework.
The first objective of the present invention is to create a thrust reverser of the above cited type wherein the torque applied to the straight guide elements is reduced, or even eliminated when the drive means of the displaceable fairing are operational.
Another objective of the invention is to configure the linear actuator and the guide elements in a manner to lower the thrust-reverser weight.
The invention attains these objectives in that the means driving the displaceable-fairing are substantially configured along the center axis of the slotted cylindrical shells.
In this manner, the design of the invention eliminates the undesirable torque. Advantageously, the slotted cylindrical shells comprise an outer wall which is firmly joined to a stationary pod structure housing in sliding manner through an elongated body, hereafter cylinder, which is firmly affixed to the displaceable fairing. The cylinder is fitted with elements cooperating with associated drive elements. The outer wall in this manner protects the cylinder displacement means from the reverse flow, in particular against buckling and pollution.
In a first embodiment, the associated drive elements include a linear control actuator.
This linear control actuator is configured with a screw rotationally driven by a kinematics element cooperating with an inside thread in the cylinder.
In one embodiment variation, the screw is configured at the end of a rod.
In another embodiment variation, an internal thread of the cylinder includes a swiveling nut fastened to the cylinder.
The linear control actuator also may be fitted with a screw firmly affixed to the cylinder and driven into translation by a kinetics unit.
In a second embodiment of the invention, the associated displacement drive elements include a kinematic element driving a gear that meshes with teeth on one side of the cylinder.
Preferably the pod and the inner structure rest on a strut, at least one guide being configured on either side of the strut.
Advantageously, the thrust reverser includes two reverser segments configured one on each side of the strut, whereby each reverser segment cooperates with one of two diametrically opposite guides defined along sides of the struts. These guides rest on the stationary structure of the turbojet-engine in diametrically opposite zones and cooperate with the rims of respective reverser semi-cylindrical segments situated at the ends of the vane-cascade fitted zones. In this manner, the linear actuators are configured outside the vane cascades and also are free from the stresses generated by the reverse flow and pollution. Consequently the reliability of the thrust-reverser assembly is greatly enhanced.
Other advantages and features of the invention are elucidated in the illustrative description below and in relation to the attached drawings.